This invention relates to fuel cells and, in particular, to a gas flow control assembly for use in fuel cell systems.
A fuel cell is a device, which directly converts chemical energy stored in hydrocarbon fuel into electrical energy by means of an electrochemical reaction. Generally, a fuel cell comprises an anode and a cathode separated by an electrolyte, which serves to conduct electrically charged ions. In order to produce a useful power level, a number of individual fuel cells are stacked in series with an electrically conductive separator plate between each cell.
Fuel cells operate by passing a reactant fuel gas through the anode, while oxidizing gas is passed through the cathode. The electrical output of the fuel cell system depends in part on the rates at which the fuel gas and the oxidizing gas are supplied to, and are carried through, the anode and the cathode, respectively, as well as on the energy content of the fuel. Therefore, in order to optimize the fuel cell performance and to obtain a desired electrical output from the fuel cell system, the flow rate at which the fuel is supplied to the cells needs to be precisely controlled.
Conventional fuel cell systems have typically employed mass flow controllers to control the flow rate of the fuel gas to the fuel cell anodes according to the power output of the fuel cell. Conventional systems have also employed an online fuel composition analyzer to determine the composition of the fuel being supplied to the fuel cell system. In particular, mass flow controllers have been used in combination with the online fuel composition analyzer to control the amount of fuel being delivered to the fuel cell based on the fuel composition determination by the composition analyzer and on the power output of the cell.
As can be appreciated, these conventional methods of controlling the flow rate of the fuel to the anodes require use of expensive and complex equipment. In addition, the reliability of the online fuel composition analyzer significantly declines when the fuel being analyzed has a high moisture content and also after prolonged operation of the analyzer. Therefore, the analyzer often needs to be re-calibrated to continue to accurately determine the fuel content. Accordingly, a means for controlling the fuel flow to the anode is needed which is accurate and reliable without requiring expensive equipment.
It is therefore an object of this invention to provide a gas flow control assembly for controlling the flow of fuel with increased reliability for prolonged periods of operation and which is not affected by the moisture levels in the fuel.
It is a further object of the invention to provide a gas flow control assembly which is capable of adjusting the fuel flow rate based on detected changes in fuel composition with increased accuracy.